Sponge materials excellent in cushioning are often used for the materials of a shoe insole. However, since a sponge material is inferior in flexibility, resilience, and restorability compared with a plastic material, it does not follow the motion of a foot. Therefore, it may have a problem of limiting a workout. Advantages of using a plastic material for the material of the shoe insole are that they fit to the foot, cooperatively act with ligaments and muscles, and act without limiting the movement of the foot, and thereby workouts can be performed more naturally. However, if the plastic material is too thick, since the ligaments and muscles of the foot are excessively constrained, the workout is limited. On the other hand, if the plastic material is too thin, a sufficient strength of the plastic cannot be obtained and, thus, a person cannot control his/her feet. Therefore, the present inventor uses a plastic material having flexibility, resilience, and restorability to develop a shoe insole which can instantaneously absorb and reduce an impact from any direction, and has already been granted a patent right (JP3,944,536B1: Patent Document 1).
Further, in order to improve the performance of the shoe insole, the use of both the sponge material and the plastic material together has already been considered. However, if the sponge material is used as the material of a body part of the shoe insole, and a component made of plastic material which is formed in an arch shape to support the arch of the foot is attached to the arch part underneath the body part which is a side contacting an inner bottom part of a shoe, since an impact from the ground surface is strongly transmitted to the underside of the foot through the component made of plastic material, there is a problem that the person feels pain in the foot. Therefore, the present inventor attaches a component made of plastic material to a body part of a shoe insole, which is made of a sponge material, at an arch part underside of the body part, devises the thickness, attached position, and shape of the component to develop the shoe insole which has supportability and hardly causes pain in the foot, and has already been granted a patent right (JP5,070,445B2: Patent Document 2).